Turbocharging an internal combustion engine can both reduce external emissions and increase the specific power output of the engine, as exhaust from the engine cylinders may be directed through a turbine and the resulting energy used to power a compressor. One example configuration integrates the exhaust ports leading from the engine cylinders and the turbine housing into the cylinder head itself.
Conventional turbocharging of an internal combustion engine includes a cylinder head which directs exhaust gasses into an exhaust manifold, which in turn directs the exhaust gasses into a turbine housing and through a turbine. The work extracted from the turbine is used to drive a compressor which increases the density of air available to power the piston portion of the engine. The turbine stage is typically a single stage radial unit with a wastegate passage in a gasoline engine.
Some modern engines utilize a concept where the exhaust ports from a plurality of cylinders are directed to a single outlet in the cylinder head. This gas is then directed through a turbine housing into the turbocharger. The exhaust manifold and turbocharger are typically constructed out of materials which are durable when exposed to repeated high temperature cycles stemming from the high temperature of exhaust gas exiting the cylinders. Such materials have a very high cost. The inventors herein have recognized that some of the cost could be reduced by removing the turbine housing and moving the turbine into the cylinder head. The cylinder head has a cooling jacket, mitigating the need for the expensive high-temperature resistant material.
A cylinder head with integral exhaust ducting and turbocharger housing is disclosed in US 2011/0173972. In this prior art example, much of the collector geometry was integrated into the cylinder head. However, this approach may be problematic, in that a large amount of aluminum cylinder head material must be cooled via engine coolant flow. This could cause an increase in heat rejected to the radiator and possibly limit vehicle performance during extreme maneuvers on hot days.
Various exemplary systems and methods are disclosed herein to at least partially address the problems described above. In one example, a turbocharger system, comprising: a bearing housing including a turbine; at least one compressor coupled to the turbine via a common shaft; and wherein the turbine comprises a stator stage and a rotor stage mounted to the cylinder head by the bearing housing and positioned in an exhaust passage of the cylinder head. The system may further comprise an axial turbine that receives exhaust gas still contained within the cylinder head. In this way, the turbocharger size may decrease, and the exhaust pulses are preserved to power the turbine.
Further, the bearing housing may further comprise a hot gas collector, and the bearing housing and hot gas collector may be one piece. In this way, the exhaust gas that passes through the turbine is cooled substantially as the energy is extracted via the turbine. The resulting lower temperature exhaust gas enables the use of lower cost materials in the bearing housing and collector, such as cast iron.
In another example, a system for an engine, comprising: a cylinder head that includes one or more exhaust passages contained within the cylinder head; a turbocharger comprising: one or more turbines including a rotor stage, one or more compressor stages and one or more shafts coupling the turbine to the compressor; and wherein the one or more exhaust passages include a first and second outlet, the rotor stage being coupled to the first outlet such that exhaust gas flowing through the first outlet causes the turbine to rotate about the shaft and further drive the compressor, the second outlet bypassing the rotor stage coupled to the first outlet, and the turbine housing is formed by the cylinder head. In this way, the system reduces the amount of cylinder head material exposed to hot gasses. The hot gas collector may be moved off the cylinder head and into a casting shared with the bearing housing. This configuration will reduce the heat rejected to the radiator to be comparable to that of an integrated exhaust manifold configuration already commonly used in turbocharged engines.
Further, the system may comprise a stator stage which may be a fabricated sheet stainless steel wheel welded into shape, or may be a cast stator. In other embodiments, the system may not comprise a stator stage, but the cylinder head may be configured to steer and accelerate the flow of exhaust gas to a desired incidence angle and velocity. In this way, the stator stage or cylinder head configuration may increase the efficiency of an axial turbine compared to prior art examples, and further the integration of a turbine into a cylinder head.
In another example, an engine cooling method comprising, within a cylinder head, combining exhaust flows from a plurality of cylinders, directing the combined exhaust flow from the cylinder head to a turbine located within a bearing housing, and directing the combined exhaust flow from the turbine to a hot gas collector within the bearing housing. In this way, the footprint of the turbocharger can be reduced, as well as reducing the need for a liquid cooling system for the turbine housing, although such cooling may be provided to some extent.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any of the disadvantages noted above or in any part of this disclosure.